In many hydraulic devices, holes in hydraulic galleries have to be sealed off. Usually, a hydraulic plug is used to do this which can take several forms.
In one known example, a tapered hole is reamed in a passage to precise dimensions and a tapered plug is pushed in to seal the passage. The plug can comprise two parts, namely a shell which seals against the internal surface of the passage and an expander (often referred to as a “pin”) which is driven into the shell by a driver tool. The expander acts as a wedge to expand the shell within the passage to seal it off.
In this first known arrangement, the shell comprises a circumferential wall of uniform thickness that has a tapered surface, both externally and internally, and a sealed end. The reamed taper of the passage, the taper of the outer surface of the shell, the taper of the inner surface of the shell and the taper of the circumferential surface of the expander, are substantially the same. In this way, when the expander is driven into the shell, the tapered outer surface of the shell seals against the reamed taper of the passage and the expander becomes wedged within the tapered cavity of the shell.
Such hydraulic plugs are described in U.S. Pat. No. 5,160,226 and are available from The Lee Company (see http://www.leeimh.com/metal/betaplug-expansion-plugs/betaplug-expansion-plug-SBP.htm for details).
In another known example, a hole of constant diameter is reamed in a passage. The transition between the reamed diameter and the passage diameter provides a step that a plug can be pushed up against during installation. As with the previous example, the hydraulic plug comprises a shell with an internal expander (“pin”). With the shell in place within the reamed part of the passage pushed up against the step, the expander can be driven into the shell's cavity to wedge the hydraulic plug in place, sealing it against the internal surface of the passage.
Hydraulic plugs of this type are also available from The Lee Company (see http://leecat.theleeco.com/ecatalog/lee-plugs/en for details).
Currently, all of these types of hydraulic plugs, while they work well and have a proven track record, they require some axial force to be applied during installation within a passage of the hydraulic gallery. As a result, the design of the component has to take into consideration that such axial forces during installation need to be balanced, not just externally but also internally. This is particularly the case where the plug engages an internal step in the passage and axial load, which counters the axial force of the expander being driven into the shell, is transferred to the plug e.g., via the corner region of the internal step between the different bore diameters. This can lead to design complexity as well as sometimes to problems of material cracking during installation. In addition, there are the additional process steps of having to ream a tapered hole or hole of larger diameter and the associated problems of removing waste from such a reaming process.
Other hydraulic plug arrangements are described in U.S. Pat. Nos. 3,825,146, 6,003,557 and US-A-2015/0202754.
It is also known from U.S. Pat. No. 3,525,365 to provide a hydraulic plug in the form of a pre-assembled cylindrical shell with a tapered bore and a frusto-conical expander. The shell can be held while the expander is pulled via a stem against a constriction in the shell. The stem comprises a weakened region which is configured to break when a predetermined force is applied to the stem. In one configuration, an open end of the shell and a base of the expander faces the pressure-side within the passage; in another, the shell is turned around relative to the frusto-conical surface of the expander so as to present a sealed end of the shell towards the pressure-side of the passage. In both cases, the tapered internal surface of the bore and the counter tapered surface of the expander match so that the expander becomes wedged along its entire length within the shell to secure the hydraulic plug within the passage.
The present disclosure can be seen to offer an improvement to the hydraulic plugs described in U.S. Pat. No. 3,525,365.